1. Field of the Invention
The present invention relates to a wafer probing system, and more particularly, to a wafer probing system including wafer probing needles, and a method of calibrating timing of signals for the wafer probing system.
2. Description of the Related Art
Generally, a plurality of integrated circuit chips are formed on one wafer. Integrated circuit chips need to be electrically connected to testing equipment in order to measure the electrical performance thereof. Integrated circuit chips are too small to be directly connected to the testing equipment. Thus, a probing card having a plurality of needles is connected to the testing equipment, and the appropriate needles contact appropriate bonding pads of a particular integrated circuit chips on the wafer. This way, the electrical performance of the integrated circuit chips is measured. Here, the testing equipment is connected to the plurality of needles via one of a plurality of signal wires. Each signal wire must have the same signal delivery characteristics. However, in many cases, each signal wire has different signal delivery characteristics because the characteristics of signal wires can vary during the manufacturing thereof. Signals used in integrated circuit chips are so sensitive that if signal wires have different characteristics, signals output from the testing equipment reach the needles at different times via the signal wires. As a result, the electrical characteristics of integrated circuit chips cannot be accurately measured. Accordingly, in order to measure the electrical characteristics of integrated circuit chips accurately, the electrical characteristics of signal wires should be accurately measured. Then, the signals, which are applied from the testing equipment to the needles, can be controlled in accordance with the accurately measured electrical characteristics of signal wires. This is referred to as signal calibration.
Conventionally, however, all of the needles are made to come into electrical contact with the bonding pads of integrated circuit chips for the signal calibration, while a wafer is loaded on a wafer chuck in a wafer probing system. Therefore, the testing equipment cannot accurately calibrate the waveforms of signals which reach the needles.
An objective of the present invention is to provide a wafer probing system that contacts wafer probing needles, one at a time.
Another objective of the present invention is to provide a method of calibrating wafer-probing needles. With this method, signals applied to the wafer probing needles can be accurately calibrated.
Accordingly, to achieve the first objective, the present invention provides a wafer probing system including a probe card on which a plurality of needles are mounted. The system includes a main support, a wafer chuck mounted on the support, and a needle contact for individually contacting one of the plurality of needles. The needle contact is comprised of a conductive signal line, and a shield line for shielding the signal line. Further, the system includes positioning means, for determining the position of the plurality of needles, being mounted on the support, moving means, for vertically moving the needle contact, being coupled to the support, and means for horizontally moving the support based on the determined position of the plurality of needles. The needle contact includes a conductive signal line and a shield line for shielding the signal line.
Preferably, the moving means includes a needle contact support, a rail for vertically moving the needle contact support, a motor for moving the rail, and a needle contact controller for controlling the motor.
In another embodiment of the present invention, a wafer probing system includes a wafer chuck on which the wafer is loaded. The system also comprises a wafer chuck support including means for moving the wafer chuck horizontally and vertically. The wafer chuck support further includes a needle contact for contacting one of the plurality of needles. Also, means for determining the positions of the plurality of needles such as a camera is mounted on the wafer chuck support. In addition, a controller is provided for receiving data on the positions of the plurality of needles from said positioning means. The controller controls the motion of the needle contact and wafer chuck based on the position information data.
Preferably, the needle contact is lower than the wafer chuck, and the shield line is grounded.
To achieve the second objective, the present invention provides a method of calibrating the timing of signals that are applied to a plurality of needles for testing a wafer, using a wafer probing system including a probe card with the needles mounted thereon, a conductive needle contact for individually contacting one of the plurality of needles, means for moving the needle contact horizontally and vertically, a signal generator electrically connected to the probe card for generating a predetermined signal, and a measurer electrically connected to the needle contact for measuring wave form and timing of a signal. The method comprises (a) selecting a needle from the plurality of needles after determining the positions of the plurality of needles, and moving the needle contact to contact the selected needle, (b) applying a predetermined signal output from the signal generator, to the selected needle via the probe card, (c) measuring time of the signal received at the selected needle via the needle contact, and (d) based on said measuring, calibrating the timing of signals which are received at the needles, after repeating the steps (a), (b) and (c) for each needle.
Preferably, the positions of the needles in step (a) are ascertained using a camera.
Therefore, in accordance with the present invention, signals applied to wafer probing needles can be accurately calibrated.